1.2 EMBRYOLOGY Flashcards
Skin structures derived from two of three primary germ layers. Which ones?
- Ectoderm
- Mesoderm
Ectoderm gives rise to ?
- epidermis
- adnexal structures
- Merkel cells
- melanocytes (neural crest)
- nerves (neuroectoderm)
Mesoderm gives rise to?
- fibroblasts
- LCs
- vessels
- inflammatory cells
When does formation of the epidermis start?
5 weeks
Epidermis 5th week of fetal life
Formation of outer periderm and inner basal epidermal layer
Epidermis 8th week of fetal life
epidermal stratification
Epidermis 9-12 weeks of fetal life
melanocytes, LCs, and Merkel cells migrate into the epidermis
Epidermis at Late second trimester
terminal differentiation, with full stratification
Formation of basement membrane, dermis, and subcutis begins at … weeks with the appearance of …
6-8 weeks
fibroblasts beneath the epidermis
When is the DEJ present?
9 weeks
primordial vasculature is formed at?
9-12 weeks
initial fat formation in subcutis begins at ?
16–18 weeks
Fetal skin dermis at 20 weeks?
mature thickness of dermis and dermal ridges present
EM of the Developing Human Epidermis at 6-8 weeks
EM of the Developing Human Epidermis at 7-9 weeks
EM of the Developing Human Epidermis at 22 weeks
dermis and hypodermis arise from the … component of the developing somite.
Dermatome
Cartoon showing the dermatome component of the somite
immunohistological features of fetal skin dermis layer
- Collagen type I is the principal component of ECM (also in adult skin)
- Collagen type III high ratio to collagen type I (than adult skin)
- Glycosaminoglycans (GAGs) level higher (than adult skin)
- Hyaluronic acid and chondroitin sulfate both higher
- Elastin was not present (found in adult skin)
What is the vernix caseosa?
white, creamy, naturally occurring biofilm covering the skin of the fetus during the last trimester of pregnancy
What is the utility of vernix caseosa?
- protects the newborn skin
- facilitates extra-uterine adaptation of skin in the first postnatal week if not washed away after birth
Vernix caseosa features
- a highly variable coating of the fetal skin
high water content (80%) largely compartmentalized within fetal corneocytes (cells forming the stratum corneum)
- develops cranio-caudally production coincides in utero with terminal differentiation of the epidermis and formation of the stratum corneum
- primarily composed of sebum, cells that have sloughed off the fetus’s skin and shed lanugo hair
- can be absent in preterm infants
- dehydration and rehydration processes occur two to four times faster at 37 degrees celcius than at room temperature[10]
- towards term fragments of vernix can mix into the amniotic fluid resulting in (normal) turbidity
- fetal swallowing of amniotic fluid mixed with fragments of vernix can also occur
- cathelicidin LL-37, alpha-defensins, and LL-37 in neutrophils
initial follicle development on the eyebrows, scalp, upper lip, and chin begins at … weeks
– spreads …
epidermal placodes (derived from ectoderm) induce underlying dermal papilla formation (derived from mesoderm)
9-12 weeks
caudally & ventrally
hair canal is fully formed at?
18–20 weeks
